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Topic # 59624 8-Apr-2010 10:06
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I'm been struggling to find a perfect resolution/refresh rate for my HTPC (without success) and it made me think; why do LCD monitors need a specific refresh rate?

I understand why CRT's had specific timings, and this has obviously carried over to the new generation of TV's.

But theoretically it should be possible to design a system where a device 'posts' an image to a digital screen whenever it wants to, and the screen shows that image until it gets another.

There would obviously be issues and limitations with doing this, but there could be some pretty major bonuses:

a bluray player could output at whatever FPS it wanted, 24, 25, 29.97, 60..

games could have the best of both worlds - Vsync without the framerate penalty, a frame would be rendered as soon as it is finished. I don't know if this would cause jerkyness though because every image could take a slightly different time to render, but it sounds good in theory! Also, if the screen required Xmilliseconds to present an image, then this could also cause problems if the game could render more quickly, but i'm sure there would be solutions.

The marketers could call it 'Native FPS' or something.

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  Reply # 316126 8-Apr-2010 11:16
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What's your point Ragnor?

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  Reply # 316231 8-Apr-2010 15:11
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The article addresses your question of "why refresh rates necessary for LCD's".




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  Reply # 316253 8-Apr-2010 15:52
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I wouldn't have thought that there was anything inherent to the design of LCD's that required them to update at a fixed rate other than the limiting factor of how fast a pixel can physically change.

The fixed refresh rates are result of the fact that LCD displays are emulating CRT's which need to repetitively refresh the display, I'm suggesting that there is no real need for this and I'm interested in whether we will see anything different in the future.

A CRT works by hitting phosphors on the screen with an electron beam causing them to light up, the phosphors fade rapidly meaning that the image must be continuously redrawn.

With LCD's (and I'm not professing to be in any way an expert here) the LCD acts as a variable filter for a constant light source. If the image doesn't change then for all intents and purposes, the screen doesn't need to do anything.

This applies more to games/real time rendering than video since it makes sense to have a fixed refresh rate for something that isn't real time/interactive.

Just been reading about Display port which sounds interesting, apparently it can allow the graphics card to directly control the LCD, might be getting closer to what i'm thinking about.

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  Reply # 316290 8-Apr-2010 18:17
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I have wondered the same thing, yes refresh rates are due to CRTs and there is no need for them any more, if the image is stationary then the data rate would be theoretically zero. Backwards compatibility is the issue here, CRTs will be around for another 20 years probably so expect this technology to be around 5-10 years after that.

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